Notifying a warning to the public in emergency situations is a legal obligation in many countries. Examples of emergency situations include natural disasters such as earthquakes, severe thunderstorms, and volcanic eruptions, industrial disasters such as explosion of a nuclear facility or a chemical factory, or a terrorist attack and war.
Conventionally, an emergency situation is notified to the public by radio broadcast and television broadcast. However, a broadcast receiver is usually a device fixed in homes, or a semi-fixed device such as a car radio. Because a user does not always carry a fixed or a semi-fixed device, the user may not be able to immediately receive the emergency information.
In response to such a problem, according to 3GPP (Third Generation Partnership Project), in a radio communication system corresponding to LTE (Long Term Evolution) for which standards are being formulated currently, an earthquake and tsunami warning system (ETWS), which is one of the public warning systems (PWS), is discussed. The ETWS is a system for transmitting emergency information regarding an earthquake or tsunami as soon as possible to a mobile terminal, by using a broadcast channel of a radio communication system (for example, see Non Patent Literature 1).